Ink jet systems, and in particular multiorifice, drop-on-demand ink jet systems, are well known in the art. A multi-orifice, drop-on-demand ink jet print head receives ink from an ink supply and ejects drops of ink through multiple orifices onto a print medium. Both thermal-type ink jet heads, which eject a drop by heating the ink to form a bubble, and impulse-type ink jet heads, which eject a drop by compressing a chamber, are common.
A thermal-type drop-on-demand ink jet print head is typically constructed by bonding together silicon wafers or hybrid thin film circuit substrates, the wafers or substrates having appropriate circuitry and chambers formed on their surfaces. An impulse-type drop-on-demand ink jet print head is typically constructed by bonding together multiple plates, the various chambers and channels being formed by appropriate holes in individual plates.
A typical impulse-type multiple orifice drop-on-demand ink jet print head has a body that defines plural ink pressure chambers which are generally planar in the sense that they are much larger in cross-section than in depth. The ink pressure chambers each have an ink inlet and an ink outlet. The ink jet print head includes an array of proximately located nozzles and passages for coupling the ink pressure chambers to the nozzles. Each ink pressure chamber is coupled by an associated passage to an associated nozzle. A driver mechanism is used with each pressure chamber to displace the ink in the ink chamber. The driver mechanism typically consists of a transducer (e.g., a piezoelectric ceramic material) bonded to a thin diaphragm. When a voltage is applied to the transducer, the transducer attempts to change its planar dimensions, but, because it is securely and rigidly attached to the diaphragm, bending occurs. This bending displaces ink in the ink-chamber, causing the flow of ink both through an inlet from the ink supply to the ink chamber and through an outlet and passageway to a nozzle.
The inlet of each pressure chamber is connected via a passage to a common ink manifold that supplies ink to several pressure chambers. An orifice is sometimes positioned between the pressure chamber and the ink manifold to reduce acoustic crosstalk between pressure chambers. The use of such a restrictor orifice is described in U.S. Pat. No. 4,680,595 of Cruz-Uribe et al. for an Impulse Ink Jet Print Head and Method for Making Same.
For high resolution printing, it is desirable that the nozzles have very small orifices and be spaced as closely as possible. Close spacing requires correspondingly small internal channels. One method of achieving close spacing is described in U.S. Pat. No. 5,087,930 of Roy et al. for a Drop-on-Demand Ink Jet Print Head, which is assigned to the assignee of the present invention. Such small orifices and internal channels in multiple orifice ink jet print heads are susceptible to clogging from particulate contamination. During assembly, particulate contamination from the assembly room environment, chromate plating flakes from ink reservoirs supplying ink to the head, and contamination from the O-rings and reservoir sealing materials are often inadvertently introduced into the interior of the print head.
U.S. Pat. No. 4,639,748 of Drake et al. for an Ink Jet Printhead With Integral Ink Filter illustrates an attempt to solve the particulate contamination problem. The patent describes a thermal ink jet print head constructed from two silicon wafers bonded together adjacent and having an integral ink filter. The integral filter, positioned between an internal ink reservoir chamber and capillary-filled ink supply channels, is formed by anisotropically and isotropically etching channels smaller than the nozzle orifices into the silicon composing the wall between the reservoir chamber and the supply manifold. Such fabrication methods are usable only for components fabricated from single crystal materials that etch at different rates along different crystal planes, because other materials cannot be anisotropically etched to create the required structures. With current metal-working technology, it is impractical to manufacture a metallic layer with filter pores having a sufficiently small opening to prevent clogging of very small nozzles.
Another ink filter for a thermal ink jet print head is described in U.S. Pat. No. 4,864,329 of Kneezel et al. for a Fluid Handling Device With Filter and Fabrication Process Therefor. The print head described by Kneezel et al. comprises two silicon wafers, one of which is etched to define ink channels, and ink manifolds having a fill hole. A wafer-sized, flat membrane filter is bonded to the silicon wafer surface over the fill holes to filter the ink before it enters the internal channels of the print head. If the print head is constructed in the "roofshooter" configuration, i.e., the nozzles are located on the top surface of a silicon wafer, the membrane filter can be positioned between the two silicon wafers and bonded to both. Such a filter must be very flat to prevent ink from seeping around the filter.
A membrane filter added to the print head increases the thickness, the difficulty of manufacturing, and cost of the print head. A membrane filter layer can also introduce mechanical stress into the head during assembly because the thermal coefficient of expansion of the mesh material may not match that of the material comprising the rest of the head. This is especially a significant problem where phase change inks are used.
Still another attempt to solve the contamination problem in print heads is illustrated in a "JOLT".RTM. Model printer by Dataproducts Corp. of Woodland Hills, Calif. The Jolt model printer places a filter fabricated from a single plate transversely across the manifold at the interface between the reservoir manifold and the print head, which increases manufacturing difficulty and does not protect against initial contamination introduced during the assembly processes.
It is generally recognized that filters are desirable to trap particulate contamination in ink jet print heads before such particulate contamination can clog orifices in the print head. As newer, higher resolution printers require increasingly smaller orifices, it has become more difficult to fabricate using conventional processes a filter having pores sufficiently small to protect such smaller orifices.